reorder modifier/constraints stack order in python
Sadly no. I ran in to the same limitation when trying to sort logic bricks.

The constraints, modifiers, and logic bricks are all read only collections.
The only way to reorder them is through the ops operators, moving one at a time, up or down one place. (which stinks for any scripting)

For constraints it is:

bpy.ops.constraint.move_up(constraint="constraintName", owner='OBJECT')
bpy.ops.constraint.move_down(constraint="constraintName", owner='OBJECT')


For modifier it is:

bpy.ops.object.modifier_move_up(modifier="modifierName")
bpy.ops.object.modifier_move_down(modifier="modifierName")


For logic bricks it is:

bpy.ops.logic.sensor_move(sensor="logicBrickName", object="objName", direction='UP')
bpy.ops.logic.actuator_move(actuator="logicBrickName", object="objName", direction='UP')
bpy.ops.logic.controller_move(controller="logicBrickName", object="objName", direction='UP')

bpy.ops.logic.sensor_move(sensor="logicBrickName", object="objName", direction='DOWN')
bpy.ops.logic.actuator_move(actuator="logicBrickName", object="objName", direction='DOWN')
bpy.ops.logic.controller_move(controller="logicBrickName", object="objName", direction='DOWN')




You probably would not want to reorder constraints or modifiers alphabetically. Both constraints and modifiers work from the top down, the order effects the out come.  

Here is an example with the exact same modifiers and default settings, just the order is reversed. Stack order makes a huge difference.